Arrangement for two-way telephony



May 7, 1929. w, wu s 1,712,062

ARRANGEMENT FOR TWO-WAY TELEPHONY Filed Nov. 23-, 1923 Source of SpeechFrequency Source of Speech Frequency- INVENTOR LTER WURST EL MW TTORNEYPatented May 7, 1929.

UNITED -STA T-E'S PATENT oF FlcE.

WALTER wunsr, OFBERLIN, GERMANY, assrcnon To ensnL sonAFrruR Danni LOSETELEGRAPHIE M. B. 11., BERLIN, GERMANY, A conrona'rron or GERMANY.

ARRANGEMENT non TWO-WAY ELEPHONY.

Application filed November 23, 1923, SeriaiNo. 676,489, and in GermanyDecember 2, 1922.

It is known that a vacuum tube transmitter, for instance, in theso-called threepoint connection, canbe used as a receiver when thereceiving 'telephone is inserted directly in the plate-filan'ientcircuit or is connected to it by means of a transformer. Thisthree-point connection is a particular form of regenerative connectionfor a three .element vacuum tube and is illustrated in the embodiment ofthe invention "disclosed in this application'merely to exemplify one oimany available regenerative circuits. This arrangement has thedisadvantage that the speech transmitted by it, which for the sake "ofconvenience will hereinafter be sometimes referred to the transmittedspeech, is reproduced witl1, eXti'ei11eloud ness in the receivingtelephone. Therefore, such an arrangement is very objectionable,particularly when the same wavelength is used -for simultaneoustransmission. and reception. It is necessary to diminish the'loudness inthe receiving telephone of the transmitted speech without diminishingthe loudness of 'the receiv'ed speech. According to the invention, thisaim is accomplished by the provision of means for limiting the currentwhich may pass through the receiving telephone, and in the event thatthe receiving telephone is connected to the plate-filament circuit otthevacuum tube by means of a transformer,

inserted in the plate-filament circuitoit the tube. The filament-heatingcurrent of the current-limiting vacuum tube can easily be regulated insuch a way that the effect of the transmitted speech on the receivingtele- 1 phone is suificiently weakened. If the cur.

rentdimiting tube is caused to operate 'at the steepest point of'ischaracteristic curve, an amplificationot weak, received signals may alsobe attained. Y 1 In'the drawing, 1 i "Fig. 1 is adiagrammaticrepresentation ot a circuit arrangement embodying the lllVGlltlOIlt. andY Fig. 2 is a diagrammaticrepresentation of a circuit arrangementalsoembodying the invention' and utilizing an additional vacuum tube as acurrent-limiting device.

Referring to Fig. 1, 0; denotes an electron discharge device having ahot cathode is, a

cold'anode (Z anda cold control electrode 8,

all enclosed within an evacuated envelope, as is well known in'the art.This tube has its circuits connected up regeneratively to generatesustained oscillations for transmitting purposes. The mode ofregenerative connection shown isknown in the art asafthree.polntconnection." v 4 w "The cn'cult which determines the 1fre-' 'quency of'the generated oscillations comprlses' -an nductance =1 and a capacity2.

The filamentary cathode 7c of the tube a is connected 'to a point ofthis inductance 1 between the ends thereof. One end of the inductance isconnected to the anode d of tube a through a stopping condenser 3 andthe other endof inductance 1 is connected to the control electrode 8 ofthe tube a thru a condenser 4. The secondary of the speech in thedrawing. This source of speech frequency may be any old and well knowndevice, such as an ordinary microphone.

The tube a receives plate current from a i source of direct current 0operating through the primary of transformer c and inductance 5. Thesecondary of transformer e is connected injseries with a currentlimiting device f and a telephoneg. I I

As explained above, when speech or any signal is impressed upon the grid8 of tube a, the generated oscillations are modulated thereby and aretransmitted to the distant station by any suitable and Well known meansas by an antenna 6 coupled to in- 1. This speech ct signal.

potential causes a corresponding speech or signalinthe telephone g,which would be very loud and undesirable if no precautions were taken toprevent it. Therefore the current limiting device f is used.

When the signal comes in from a distant station, the signal is impressedupon the circuits of the tube a; from the antenna 6. Due to thedetecting action of said tube, the sig nal is V detected and heard withthe telephone 9.

The circuitshown in Fig. 2 is similarto that shown in Fig. 1, similarreference characters referring to similar elements in these figures. InFig. 2, however, the vacuum tube 72 having a cathode it, controlelectrode a, and anode p, is used as the current limiting device. Thegrid-filament circuit of tube It is connected across the secondary oftransformere. The filament 25 and anode p of the tube 7b are preferablyconnected with the filament-heating circuit of the transmitting tube aso as to cause the filamentheating battery 2' of the transmitting tubea; to supply both heating current to the filament t of the tube It andanode voltage to the plate-filament circuit of said tube. The strengthof current which may pass through the tube It depends upon the number ofelectrons emitted from its 'filament t, which, in turn, depends upon thedegree to which the filament is heated. Accordingly, the currentpassingthrough the tube 71, and the loud ness ofsound which may beproduced in .the receiving telephone in the plate-filament circuit ofsaid tubemay be readily regulated by suitably controlling the amount ofcurrent supplied to the filament t of the tube h from the battery 2'. y

The limiting action of tube It for large currents and its amplifieraction for small currents is obtained by arranging the constants of tube7a in such manner that for voltages impressed-onit-s grid exceeding acertain predetermined value, the corresponding plate current of tube itcan become no larger. In other words, the tube It saturates at a certainpredetermined value of grid voltage. v

. For impressed grid voltages less than this predetermined value thetube will giveits usual amplifier action, thus acting as an amplifierfor small voltage Having described my invention, what I claim is:

An arrangement for two way telephony comprising a vacuum tube, controlelectrode and anode circuits associated therewith and regenerativelycoupled to form an oscillation generator, an antenna circuit associatedwith said oscillation generator forradiating energy therefrom or forimpressing received energy thereon, a speech modulation circuit coupledto the control electrode circuit of said oscillating vacuum tube, atelephone receiver circuit coupled to the anode circuit of saidoscillating vacuum tube, and a second vacuum tube in said telephonereceiver circuit arranged for limiting the energy applied to thereceiver by saturating at an energy value of the order of magnitude ofthat flowing uponthe reception of normal remotely transmit-ted signals.7 i

WALTER ,W'URST.

